The number of echoes combined into a single image or image set in multiple echo imaging sequences or echo-train techniques such as rapid acquisition with relaxation enhancement (RARE), fast-spin echo (FSE), and turbo spin-echo (TSE). In RARE imaging, the ETL typically equals the acceleration factor.
As for tooth pain, it is caused by a reaction of the nerves inside a tooth's pulp chamber with the severity dependent upon the type and degree of the stimulus. What follows are some examples of symptoms you may be feeling and their possible causes.
The dental causes of tooth pain fall into several categories: 1  Damage: Damage to the tooth is a common cause of tooth pain. For example, teeth that are chipped or broken due to trauma can cause tooth pain. 2  Decay: Tooth decay is one of the most common causes of tooth pain, and it has several degrees of severity.